PROJECT SUMMARY Anterior segment dysgenesis (ASD) phenotypes comprise a group of disorders characterized by structural abnormalities involving the iris, cornea, iridocorneal angle, and lens, and associated with a high risk of visual impairment through glaucoma, corneal opacification and other complications. This group of conditions includes Axenfeld-Rieger anomaly (ARA) and syndrome (ARS), aniridia, Peters anomaly/corneal opacities, and pediatric glaucoma (even in the absence of visible ASD, believed to be associated with abnormal development of the outflow tract). We identified mutations in PITX2 as the cause of ARS and then expanded associated phenotypes to other ASDs; the second ARS gene, FOXC1, was also subsequently shown to explain diverse ASD phenotypes and a recent study implicates it in POAG in multiple populations. PITX2 and FOXC1 play a major role in ASD, explaining 40-60% of ARA/ARS with the majority of negative cases remaining unexplained. For the broader ASD spectrum, the success rate for identifying a genetic diagnosis varies in populations but, likewise, continues to be incomplete (less than 50%) necessitating the identification of novel mechanisms. The overall goal of this project is to uncover mechanisms of ASD and associated glaucoma/visual impairment by investigating diverse aspects of this disease: human phenotype, mechanisms associated with PITX2/FOXC1, and novel gene discovery through exome/genome human studies and CRISPR-Cas9 editing in zebrafish. Specifically, we aim: 1) To reveal the full range of ocular anomalies in ?anterior segment dysgenesis? disorders. High-resolution imaging in individuals with ASD will investigate the possibility of posterior segment defects and their contribution to vision loss. This aim will provide new insight into human disease as suggested by our initial data which identified novel features in two (out of two) ARS patients; 2) To define developmental roles and pathways of FOXC1 and PITX2 and explore their contribution to human disease. This aim will identify targets of foxc1 in zebrafish using recently developed lines and explore regulatory elements of this gene. Our preliminary results from one of the foxc1 regulatory deletion mutants show a strong glaucoma phenotype, different from the loss-of-function line, and is likely to become the first zebrafish embryonic glaucoma mutant. The obtained results will be analyzed together with the previously generated pitx2 data to reveal common pathways. Since our earlier data indicate dysregulation of the WNT pathway as a major outcome of pitx2 deficiency, its role in the eye phenotype will be further examined; and finally, 3) To discover novel factors with a role in anterior segment dysgenesis by utilizing exome/genome data from families affected with ASD and genome editing-based modeling in zebrafish. The identified factors will be evaluated for their position in known pathways using our previously developed resources. The strength of our application is in its innovative approaches, the unique resources that we generated, robust approach, and the outstanding expertise of our team in vertebrate genetics, eye development and ASD phenotypes.